Atomic layer deposition (ALD) processes are useful for the creation of thin films, as described by M. Ritala and M. Leskela in “Atomic Layer Deposition” in Handbook of Thin Film Materials, H. S. Nalwa, Editor, Academic Press, San Diego, 2001, Volume 1, Chapter 2. Such films, especially metal and metal oxide films, are critical components in the manufacture of electronic circuits and devices.
In an ALD process for depositing copper films, a copper precursor and a reducing agent are alternatively introduced into a reaction chamber. After the copper precursor is introduced into the reaction chamber and allowed to adsorb onto a substrate, the excess (unadsorbed) precursor vapor is pumped or purged from the chamber. This process is followed by introduction of a reducing agent that reacts with the copper precursor on the substrate surface to form copper metal and a free form of the ligand. This cycle can be repeated if needed to achieve the desired film thickness.
ALD differs from chemical vapor deposition (CVD) in the decomposition chemistry of the metal complex. In a CVD process, the complex undergoes pyrolytic decomposition on contact with the surface to give the desired film. In an ALD process, the complex is not completely decomposed to metal on contact with the surface. Rather, formation of the metal film takes place on introduction of a second reagent, which reacts with the deposited metal complex. In the preparation of a copper film from a copper(I) complex, the second reagent is a reducing agent. Advantages of an ALD process include the ability to control the film thickness and improved conformality of coverage because of the self-limiting adsorption of the precursor to the substrate surface in the first step of the process.
Ligands for use in ALD processes are stable with respect to decomposition and be able to desorb from the complex in a metal-free form. Following reduction of the copper, the ligand is liberated and removed from the surface to prevent its incorporation into the metal layer being formed.
S. G. McGeachin, Canadian Journal of Chemistry, 46, 1903-1912 (1968), discloses the synthesis of 1,3-diimines and metal complexes of thereof, including bis-chelate or homoleptic complexes of the form ML2.
U.S. Pat. No. 6,464,779 discloses a Cu atomic layer CVD process that requires treatment of a copper precursor containing both oxygen and fluorine with an oxidizing agent to form copper oxide, followed by treatment of the surface with a reducing agent.
WO 2004/036624 discloses a two-step ALD process for forming copper layers comprising forming a copper oxide layer from a non-fluorine containing copper precursor on a substrate and reducing the copper oxide layer to form a copper layer on the substrate. Copper alkoxides, copper β-diketonates and copper dialkylamides are preferred copper precursors. The reducing agent is a hydrogen (H2) containing gas.
US 2003/0135061 discloses a dimeric copper(I) precursor which can be used to deposit metal or metal-containing films on a substrate under ALD or CVD conditions.
WO 2004/046417 discloses the use of dimeric copper (I) complexes comprising amidinate ligands for use in an ALD process.